In travelling wire EDM apparatus, it is known to thread the end of the electrode wire through an aperture or through the machined slot in the workpiece by means of a stream of fluid flowing through the aperture in the direction of threading of the electrode wire.
Such arrangements are described for example in Swiss Patent No. 559,599 and U.S. Pat. No. 3,987,270. Those patents disclose devices for forcibly passing the end of the electrode wire through a starter hole by a fluid stream, for example a stream of water, flowing under a very high pressure. Correct functioning of such devices present however many problems of construction and adjustment which are relatively difficult to solve. In effect, in order to achieve a pulling effect, it is necessary to evacuate from the machining zone any fluid there present. It is difficult to achieve sufficient accuracy in aim to drive the wire through a very narrow starter hole or aperture in the workpiece. In addition, after the wire has been introduced through the starter hole or aperture, it is difficult to engage the end of the wire into the conveying mechanism pulling the wire through the machining zone.